1. Field of the Invention
The present invention is directed to a torque converter having a converter housing that is connectable to a driving unit, an impeller wheel fixedly connected to the converter housing, a turbine wheel arranged in the converter housing and rotatable with respect to the converter housing about an axis of rotation and having a turbine wheel shell and a turbine wheel hub that is connectable with a converter driven shaft.
2. Description of the Related Art
In automotive engineering, a torque converter is frequently used in connection with automatic transmissions. A problem exists in prior art torque converters in that power loss is generated when the vehicle is stationary and the engine is running because an impeller wheel which is driven by the converter housing delivers a work fluid provided inside the converter to the turbine wheel and a stator wheel. In these prior art devices, the turbine wheel is connected directly to the output shaft. Since the vehicle is held still by brakes, the power loss is generated by the stator rotating against a turbine wheel that is held still. In a known solution which prevents the generation of power loss, a clutch is installed between the driving unit and torque converter which completely separates the converter and the gear unit connected following the converter from the driving unit when the vehicle is stationary. A problem with this solution is that the converter housing and the components which are fixedly connected therewith generally form a flywheel mass for the engine and therefore facilitate a quiet and true running of the engine. Uncoupling the converter housing, and accordingly the entire converter, from the driving unit may result in rough or out-of-true running of the engine especially in the low speed ranges of the engine.
Another known solution is to provide a clutch which separates the torque converter from the gear unit connected downstream of the torque converter. In this solution, the torque converter remains coupled with the driving unit in the lower speed range such, for example, as when the vehicle is stationary. To prevent the rough running of the unit, the turbine wheel in this case must carry along the entire mass of those components connecting the torque converter to the clutch. Since a clutch of this kind is generally arranged at the input side of the transmission, the transmission input shaft is rotated with the turbine wheel. This configuration results in a power loss because the torque converter and the additional mass of the transmission shaft must be rotated.
In hydrodynamic torque converters, an unchangeable converter characteristic is predetermined by the given vane geometry of the turbine wheel vanes on the one hand and of the impeller vanes on the other hand. This converter characteristic is generally designed for optimum performance in the warm operating state of the engine or of the gear oil. When starting in the cold state, the engine can be loaded so highly due to an overly hard design of the impeller that the engine can no longer run up to speed correctly or runs out-of-true. There is even a risk that the engine will stall. A possible solution to this problem is a configuration of vane geometry that is a compromise between cold running behavior and warm running behavior. However, this compromise has the disadvantageous effect that when the unit is running in the warmed-up condition the inherent transmission capacity of the converter is not utilized causing an increase in fuel consumption.